June and Harry Potter

I gave my wife and son a trip to orlando June 18- June 30. So now I'm beginning to plan. We have never been to Universal's Harry Potter land but are huge fans of the books and the movies. This is a must see, but we only plan to spend 1 day. As of now, our calendar is free. What is the best day of the week to visit? And why do you think its the best day. And do you think we need to spend more time. We are not a big roller coaster family.